A tree delimbing process involves removing the limbs (i.e., sticks or branches) of a tree (i.e., stick) from its stem. Generally, three conventional methods for delimbing are presently used in the logging industry. The conventional methods are (1) chainsaw delimbing, (2) pull-through delimbing, and (3) gate delimbing. Cutting branches during the delimbing process often results in a sudden release of stored energy, which may cause the branch and/or the entire tree to jump dangerously as the cut is underway or nearly complete. Moreover, one or more branches undergoing the delimbing process may be supporting the tree, and the tree can fall or roll when the branch is cut. For these reasons, delimbing is a skilled operation requiring careful safety considerations. The delimbing process includes at least one saw cut to top off an upper portion of the tree. For purposes of the present description herein, the terms “stick” and “tree” may be synonymous, but preferably the convention that will generally be applied below will be that a “tree” is not-yet-delimbed (field pre-processed) while a “stick” has been topped and delimbed (field post-processed).
After the delimbing process, the sticks are sent to a mill for further processing. To improve the overall efficiency of the logging process, many mills have strict specifications of what type of timber will be accepted for further processing. All mills have a specific minimum top size that is acceptable for customers. Mills that produce lumber have specifications that limit the amount of defects in trees and may also require a minimum top size. Some examples of defects include: knots, rot, crook, and sweep. Currently, a loader operator is approximately thirty (30) feet away from the delimber/saw and their vision is limited by the delimber/saw itself. When you combine the distance from the delimber/saw and the fact that the delimber/saw blocks the operator's vision in most cases, this makes it difficult for the operator to accurately determine where the tree should be cut to eliminate defects and meet the minimum top size.
In most cases, there is more than one minimum top size needed to process trees in a timber operation. A timber operation usually has several different products that require sorting. Each product may require a different minimum top size. Accordingly, accurate delimbing can result in greater mill acceptance, less waste, and more efficient mill processing.
Chainsaw delimbing is a manual process performed by one or more lumberjacks with a chainsaw. While the lumberjack has a close-up view of the branches and the tree top to line up the respective saw cuts, it must be appreciated that the terrain, weather, tree orientation and various other factors may minimize the likelihood that even a skilled lumberjack may achieve an ideal cut or at least do so repeatedly. Further, chain saws are inherently dangerous, thus the cost of a skilled lumberjack and potential injury implications of chainsaw delimbing make it a less-than-preferred process.
Pull-through delimbing involves either a stand-alone delimber or a trailer-mounted pull-through delimber. These delimbers have a set of pressure sensitive knives that close around the tree at which point a skidder or loader, respectively, pulls the tree through and the branches are cut off. In addition, these delimbers have a saw that can be selectively lowered to top off the tree.
FIG. 1 shows a conventional tree harvesting system 10 having a loader 12 and a delimber 14. The loader 12 includes a cab 16, a boom 18 and grapples 20 for lifting and holding large loads or single logs 22 while they are pulled or pushed through the delimber 14. The cab 16 houses an operator (not shown). Sticks may be placed on a rack 24. The configuration of the boom 18 permits the operator to be remotely and safely located in the cab 16 and away from the cutting areas during the delimbing process.
FIG. 2A shows the delimber 14 having a cradle structure or cradle frame 26 configured with a throat opening 28 that receives the log 22 (not shown). A plurality of knives 30 for cutting the branches are located proximate the throat opening 28. FIG. 2B shows the delimber 14 having a deployable saw 32 that pivots relative to the cradle frame 26 to cut the log 22. When not in use, the saw 32 may be rotated into a cavity formed in the cradle frame 26 so that the saw 32 will be protected from the elements.
When harvesting trees using the pull-through delimbing process, the operator, who is located in the cab of the loader, cannot see the point where the saw contacts the tree for the topping off process, which may result in sticks and/or tops that are poorly or incorrectly cut. The operator is removed from an interaction point of the saw and the tree by the nature of the equipment (e.g., the length of the boom). Most pull-through delimbers have a device for measuring the length of the tree after delimbing.
Gate delimbing involves a steel frame that is normally placed just before a landing. A grapple skidder pushes the tree backward through the gate to break off the majority of the limbs. While this may be a fast process and may avoid slush piling up at the landing, gate delimbing may result in unwanted breakage as well as poor quality delimbing.